The present invention relates to the field of stimulating the osteogenesis of a traumatized bone being fixed by means of a bone stabilizing implant. In particular the present invention relates to a device for electrically stimulating the osteogenesis of a traumatized bone being fixed by means of a bone stabilizing implant such as a bone plate or bone nail.
Further, the present invention relates to a medical system for electrically stimulating the osteogenesis of a traumatized bone, wherein the medical system takes benefit from an osteogenesis stimulation device as described above.
It is known that the growth of bone tissue can be promoted by applying an electric field, in particular by a low-frequency alternating field, to the region wherein an improved osteogenesis is desired.
DE 31 32 488 A1 and U.S. Pat. No. 4,195,367 disclose devices for stimulating the bone growth by the method of Kraus-Lechner, which can be used in conjunction with a medullary nail or an osteosynthesis plate. The stimulation devices of DE 31 32 488 comprise a pick-up coil in which a low-frequency alternating voltage can be induced by means of a low-frequency electromagnetic alternating field. Thereby, the voltage is fed to two tissue electrodes one of which may comprise the osteosynthesis implant.
U.S. Pat. No. 6,778,861 B1 discloses a bone screw comprising a device for stimulating bone growth. The bone screw comprises a hollow, tubular shaft consisting of metal, such as titanium, the shaft having a head at one end and an external thread at the other end. The head has a hexagonal recess for inserting a turning tool. An electrically insulated metallic end-piece, which tapers in the direction of the end in the form of a cone or a pointed arch, is inserted into the other end of the shaft. A receiving coil is located in the hollow shaft whereby the terminals of the coil being electrically coupled to the shaft and to the end-piece. The space between the end-piece and the end of the shaft as well as the interior of the shaft are filled with a biocompatible insulating compound. A low-frequency electric voltage can be induced in the receiving coil by an external primary coil, which is coupled to an oscillation generator. The electric voltage generates a growth-promoting current in the surrounding tissue whereby the shaft and the end-piece act as tissue electrodes.
CH 662 279 A5 discloses another device for stimulating bone growth. Thereby, a high-frequency alternating voltage generated by a high-frequency oscillator is amplitude-modulated with the output voltage of a low-frequency oscillator. The amplitude-modulated output voltage of the high-frequency oscillator is applied to outer electrodes of the stimulation device via an impedance-matching transformer and conductors. Two parts of a broken bone are held together mechanically by means of screws. One screw is attached to a metal layer via an insulator and electrically connected to the metal layer via a diode. The metal layer forms an inner electrode. The other screw penetrates a metal plate, which forms a further internal electrode and is connected in an electrically direct fashion to the metal plate. The high-frequency oscillation serves to transmit the low-frequency energy of the low-frequency oscillator to the screws via a capacitor formed by the one external electrode and the one internal electrode as well as a further capacitor formed by the other external electrode and the other internal electrode. The amplitude-modulated high-frequency voltage is demodulated by the diode, such that at the screws the low-frequency voltage required for stimulating the tissue region between the screws is applied to the screws.
U.S. Pat. No. 4,430,999 discloses a cathode assembly for use in conjunction with an internal fracture fixation device for the purpose of stimulating osteogenesis respectively bone growth within a fracture site. The assembly comprises a carrier made from an implantable non-conductive material containing a cathode with a conductive cable leading from the cathode to the patient's electrical bone growth stimulation apparatus. The carrier is mountable on the fixation device for maintenance at the desired location. A sleeve carrier contains a plurality of ports, which allows a current generated by an electrical stimulation device to flow through the cable to the cathode where it is evenly distributed through the ports to the bone tissue. The sleeve can be slipped onto a fracture fixation device, such as a compression hip screw, and is located on the device such that the sleeve containing the cathode lies across the fracture site.
The known cathode assembly has the disadvantage that it requires a percutaneous wired connection between the electrical bone growth stimulation apparatus and the cathode assembly such that the risk of infections is increased. A further disadvantage is that mounting the cathode assembly on the fixation device in the course of a surgery is a rather complicated procedure such that the risk of a surgery trouble or a surgery mistake is also increased.
U.S. Pat. No. 4,421,115 discloses an electrification attachment for an osteosynthesis implant, which permits electric stimulation of tissue and specifically bone tissue to which an osteosynthesis plate or a bone nail has been attached. The attachment provides electrical energy by induction from an external induction coil. A support body is provided for attaching association with the osteosynthesis implant. At least one induction coil is embedded in, or secured to the body. Electrodes are connected to the windings of the coil, one of which is connectable with a conductive portion of the osteosynthesis implant, the other electrode being exposed to bone tissue of the patient. However, the disclosed electrification attachment has the disadvantage that due to the geometry of the electrode being exposed to the bone tissue only a rather weak electric field can be applied to the damaged bone region such that the bone healing effect is comparatively small.
There may be a need for providing an osteogenesis stimulation device, which can be easily inserted together with a bone stabilizing implant and which provides for an improved bone healing effect.